Photonic crystal resonators, such as photonic crystal microcavities or, in other words, light-confining defects, may be used for various applications, for example, for light emitting or lasing. They also can be used in gyroscopes when arranged in a coupled resonator waveguide [1].
Coupled resonator waveguides (CRWs) or, in other words, coupled cavity waveguides (CCWs), are useful elements in various optical applications. CRWs in several aspects are different from typical waveguides. In classical systems, the phase accumulation due to propagation of light is essentially that of a plane wave or a fiber-optical mode. However, in CRWs, signal propagation is based on coupling (also referred to as hopping or tunneling) of light from one resonator (e.g. a microcavity) to the next resonator. Thus, in CRWs the propagation mechanism is quite different from that of a conventional fiber or laser resonator. The second important difference of CRWs from “plane wave” waveguides is associated with the dispersion relation and bandwidth of propagating light. In contrast to relatively weak dispersion and large bandwidth of plane waves or fiber optical modes, CRW propagation modes, constructed via interaction of the local tunneling (i.e. coupling) effects, are relatively narrow-band and possess a Floquet-Bloch-type character, when the CRW is of a periodic structure. These features of CRWs can be utilized, for example, in CRW devices implemented by defects in photonic crystals or by chains of ring resonators.
The Sagnac effect, in its original definition, is known as the relative phase shift between two beams of light that have traveled an identical curvilinear path in opposite directions in a rotating frame. The path is determined by the media (made therewithin). Phase accumulation for the beam co-directed with the rotation differs from the accumulation for the beam which is counter-directed with rotation. The Sagnac effect is used extensively in practice. For example, highly accurate and sensitive rotation measurement devices are designed based on this effect. In particular, for navigation modern fiber-optic gyroscopes, known as Sagnac interferometers, are often used.
The Sagnac effect occurring in slow-wave structures consisting of a set of coupled non-degenerate micro-cavities is described particularly in the article [1] of the inventor of the present patent application.